The present invention relates to data storage systems and, more particularly to the use of microactuators in a disc drive head positioning apparatus.
Disc drive data storage systems use rigid discs which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor which causes the discs to spin and the surfaces of the discs to pass under respective disc head sliders. The sliders carry transducers which write information to and read information from the disc surfaces. The slider and transducer are often together referred to as a xe2x80x9cheadxe2x80x9d. Each slider is supported by a track accessing arm and a suspension. The track accessing arms move the sliders from track to track across the surfaces of the discs under the control of electronic servo control circuitry for track following operations.
The suspension connects the track accessing arm to the slider. The.suspension provides a preload force through a relatively rigid load beam which forces the slider toward the disc surface. Additionally, the suspension is flexible in the slider pitch and roll directions to allow the slider to follow the disc topography. This pitch and roll flexibility is obtained from a gimbal structure, which can be integral with the load beam or a separate piece part that is welded to the load beam.
Microactuators have been proposed for providing xe2x80x9cfinexe2x80x9d position control of the slider and transducer in disc drive servo systems. These microactuators have been positioned at various locations along the suspension or between the suspension and the head. Microactuated suspensions often use piezoelectric devices, which exhibit a change in length with a change in an applied voltage. This change in length is used to move the slider and transducer relative to the disc surface. However, piezoelectric devices are also known to exhibit hysteresis when driven with a voltage control driver. Hysteresis is particularly troublesome in disc drive servo systems since it limits the accuracy at which the head can be positioned within a desired data track.
The present invention addresses these and other problems in the prior art.
One aspect of the present invention relates to a disc drive head positioning apparatus, which includes a head, a suspension which supports the head, a piezoelectric microactuator which is operatively coupled to the suspension, and a charge feedback driver which is operatively coupled to the piezoelectric microactuator.
In one embodiment, the charge feedback driver includes a position command input for receiving a position command signal, a position control output, a charge driver circuit and a charge feedback circuit. The position control output is coupled across the piezoelectric microactuator. The charge driver circuit is coupled between the position command input and the position control output. The charge feedback circuit has a charge feedback input coupled to the position control output and a charge feedback output coupled to the charge driver circuit, The charge feedback circuit is adapted to sense charge delivered to the microactuator through the position control output.
The charge feedback circuit can include a current sensing resistor, which is coupled in series with the position control output and forms the charge feedback input, and a voltage measurement circuit, which is coupled across the current sensing resistor and has a voltage feedback output which is coupled to the charge feedback output.
The driver circuit can include an operational amplifier, a pull-up transistor and a pull-down transistor. The operational amplifier has first and second amplifier inputs which are coupled to the position command input and the charge feedback output, respectively, and an amplifier output. The pull-up transistor is coupled to a first terminal of the position control output and has a control terminal which is coupled to the amplifier output. The pull-down transistor is coupled to the first terminal of the position control output and has a control terminal which is coupled to the amplifier output.
The disc drive head positioning apparatus can further include a charge reset circuit, which has a charge reset command input, and first and second switches. The reset command input receives a reset signal having an active state and an inactive state. The first switch is coupled between the position control input and the charge driver circuit and has a closed state when the reset signal is in the inactive state and an open state when the reset signal is in the active state. The second switch is coupled across the microactuator and has an open state when the reset signal is in the inactive state and a closed state when the reset signal is in the active state.
The disc drive head positioning apparatus can further include an error feedback circuit coupled between the charge feedback output and the position command input. The error feedback circuit includes an integrator, an error correction circuit and a summing element. The integrator integrates the charge feedback output for a selected time period and generates an integrator output that represents the charge delivered to the piezoelectric microactuator. The error correction circuit is coupled to the integrator output and to the position control input and is adapted to generate a correction signal that represents a comparison between a commanded displacement of the piezoelectric microactuator corresponding to the position command signal and an actual displacement of the piezoelectric microactuator corresponding to the integrator output. The summing element sums the position command signal and the correction signal to generate a corrected position command signal that is applied to the driver circuit. The error correction circuit can further include an offset control input, wherein the correction signal is adjustable through the offset control input.
In an alternative embodiment, the charge feedback circuit includes a reference capacitor and a voltage feedback amplifier. The reference capacitor is coupled in series with the piezoelectric microactuator, between first and second terminals of the position control output, and forms a reference node therebetween. The voltage feedback amplifier has a non-inverting input coupled to the position command input, an inverting input coupled to the reference node, and an output coupled to the driver circuit.
In another alternative embodiment, the charge feedback circuit includes a voltage feedback amplifier and a current mirror. The voltage feedback amplifier has an inverting input, a non-inverting input coupled to the position command input, and an output coupled to the driver circuit. The current mirror has first and second legs, wherein the first leg is coupled in series with a reference capacitor across the position control output, the second leg is coupled in series with the microactuator across the position control output, and the inverting input is coupled to a reference node between the reference capacitor and the first leg.
Another aspect of the present invention relates to a method of controlling radial position of a head relative to a storage medium in a disc drive. The method includes supporting the head relative to the storage medium, and receiving a position command signal indicative of a commanded radial position for the head. Based on the position command signal, a microactuator drive signal is generated and used to vary an actual radial position of the head through a piezoelectric microactuator. A representation of the charge delivered to the piezoelectric microactuator by the drive signal is measured, and the microactuator drive signal is varied based on the measured representation of the charge.
Another aspect of the present invention relates to a disc drive head positioning apparatus, which includes a head and a microactuator. The microactuator controls a radial position of the head relative to a storage medium through a piezoelectric microactuator element based on a position command signal and a representation of the charge delivered to the piezoelectric microactuator element.